fix(telemetrygen): fix histogram data points to comply with spec (#39025)

#### Description
The HistogramDataPoint message has a couple of clear rules: the Count
field must equal the total count of all buckets (if present), and the
length of the bucket array must be one greater than the length of the
boundary array. This fixes the telemetrygen histograms to conform to
these rules.

See
https://github.com/open-telemetry/opentelemetry-proto/blob/main/opentelemetry/proto/metrics/v1/metrics.proto#L443

Author: ianwilkes

.chloggen/telemetrygen-histogram-fix.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: telemetrygen
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Fixes invalid HistogramDataPoint messages generated by telemetrygen.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [39025]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: The bucket count and total count are now correct.
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [api]

cmd/telemetrygen/pkg/metrics/worker.go

@@ -31,48 +31,52 @@ type worker struct {
 	index                  int                          // worker index
 }
 
+// We use a 15-element bounds slice for histograms below, so there must be 16 buckets here.
+// From metrics.proto:
+// The number of elements in bucket_counts array must be by one greater than
+// the number of elements in explicit_bounds array.
 var histogramBucketSamples = []struct {
 	bucketCounts []uint64
 	sum          int64
 }{
 	{
-		[]uint64{0, 0, 1, 0, 0, 0, 3, 4, 1, 1, 0, 0, 0, 0, 0},
+		[]uint64{0, 0, 1, 0, 0, 0, 3, 4, 1, 1, 0, 0, 0, 0, 0, 0},
 		3940,
 	},
 	{
-		[]uint64{0, 0, 0, 0, 0, 0, 2, 4, 4, 0, 0, 0, 0, 0, 0},
+		[]uint64{0, 0, 0, 0, 0, 0, 2, 4, 4, 0, 0, 0, 0, 0, 0, 0},
 		4455,
 	},
 	{
-		[]uint64{0, 0, 0, 0, 0, 0, 1, 4, 3, 2, 0, 0, 0, 0, 0},
+		[]uint64{0, 0, 0, 0, 0, 0, 1, 4, 3, 2, 0, 0, 0, 0, 0, 0},
 		5337,
 	},
 	{
-		[]uint64{0, 0, 1, 0, 1, 0, 2, 2, 1, 3, 0, 0, 0, 0, 0},
+		[]uint64{0, 0, 1, 0, 1, 0, 2, 2, 1, 3, 0, 0, 0, 0, 0, 0},
 		4477,
 	},
 	{
-		[]uint64{0, 0, 0, 0, 0, 1, 3, 2, 2, 2, 0, 0, 0, 0, 0},
+		[]uint64{0, 0, 0, 0, 0, 1, 3, 2, 2, 2, 0, 0, 0, 0, 0, 0},
 		4670,
 	},
 	{
-		[]uint64{0, 0, 0, 1, 1, 0, 1, 1, 1, 5, 0, 0, 0, 0, 0},
+		[]uint64{0, 0, 0, 1, 1, 0, 1, 1, 1, 5, 0, 0, 0, 0, 0, 0},
 		5670,
 	},
 	{
-		[]uint64{0, 0, 0, 0, 0, 2, 1, 1, 4, 2, 0, 0, 0, 0, 0},
+		[]uint64{0, 0, 0, 0, 0, 2, 1, 1, 4, 2, 0, 0, 0, 0, 0, 0},
 		5091,
 	},
 	{
-		[]uint64{0, 0, 2, 0, 0, 0, 2, 4, 1, 1, 0, 0, 0, 0, 0},
+		[]uint64{0, 0, 2, 0, 0, 0, 2, 4, 1, 1, 0, 0, 0, 0, 0, 0},
 		3420,
 	},
 	{
-		[]uint64{0, 0, 0, 0, 0, 0, 1, 3, 2, 4, 0, 0, 0, 0, 0},
+		[]uint64{0, 0, 0, 0, 0, 0, 1, 3, 2, 4, 0, 0, 0, 0, 0, 0},
 		5917,
 	},
 	{
-		[]uint64{0, 0, 1, 0, 1, 0, 0, 4, 4, 0, 0, 0, 0, 0, 0},
+		[]uint64{0, 0, 1, 0, 1, 0, 0, 4, 4, 0, 0, 0, 0, 0, 0, 0},
 		3988,
 	},
 }
@@ -117,9 +121,13 @@ func (w worker) simulateMetrics(res *resource.Resource, exporter sdkmetric.Expor
 				},
 			})
 		case MetricTypeHistogram:
+			var totalCount uint64
 			iteration := uint64(i) % 10
 			sum := histogramBucketSamples[iteration].sum
 			bucketCounts := histogramBucketSamples[iteration].bucketCounts
+			for _, count := range bucketCounts {
+				totalCount += count
+			}
 			metrics = append(metrics, metricdata.Metrics{
 				Name: w.metricName,
 				Data: metricdata.Histogram[int64]{
@@ -130,7 +138,7 @@ func (w worker) simulateMetrics(res *resource.Resource, exporter sdkmetric.Expor
 							Time:       time.Now(),
 							Attributes: attribute.NewSet(signalAttrs...),
 							Exemplars:  w.exemplars,
-							Count:      iteration,
+							Count:      totalCount,
 							Sum:        sum,
 							// Bounds from https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#explicit-bucket-histogram-aggregation
 							Bounds:       []float64{0, 5, 10, 25, 50, 75, 100, 250, 500, 750, 1000, 2500, 5000, 7500, 10000},